1. Field of the Invention
The present invention relates to a system for measuring the wall thickness of generally oval shaped containers and, more specifically, includes means for adjusting the thickness measurement for changes in diameter resulting from the non-round nature of the container. The invention also relates to measurement of container diameters.
2. Description of the Prior Art
It has long been known, with respect to containers, such as glass and plastic bottles and jars, to inspect the same for compliance with various specifications, such as shape, dimensions, wall thickness, and any other departures from the specified parameters. In connection with such inspection, it has been known to use a sampling technique wherein periodically a sample container is removed from the production line and inspected. For glass containers, the measurement of thickness, for example, has been accomplished by hand-held capacitive or ultrasonic thickness measuring instruments. In the alternate, destructive testing as by taking a sample and cutting it into pieces with subsequent mechanical measurement has also been known. While such sampling techniques can provide accurate measurements, they suffer from the disadvantage of using samples and the need to make statistical inferences based upon the results of such sampling. As every container is not inspected, it is possible that a number of defects will go undetected. This can result not only in loss of the container, but loss of the product to be placed in the container and, perhaps, injury to the consumer or other user.
It has been known to employ capacitive means for automatically inspecting wall thickness of containers made of dielectric materials with inspection of each container, as distinguished from sampling techniques, being employed. See, generally, U.S. Pat. Nos. 2,573,824; 4,820,972; 4,862,062; 4,870,342; 4,930,367; 4,965,523; and 4,972,566. It has also been known, in such a context, to provide a plurality of sensors which cooperate with oscillator means to produce an output voltage responsive to capacitance changes which voltage is employed to determine container wall thickness. See, for example, U.S. Pat. Nos. 4,862,062; 4,870,342; 4,965,523; and 4,972,566.
It has also been known to provide such a system wherein a plurality of containers rotating by and being urged into intimate contact with a plurality of sensors may be inspected simultaneously. See U.S. Pat. No. 5,097,216 which is owned by the assignee of the present application.
These prior systems were directed toward inspecting round containers made of a dielectric material. When non-round annular containers, such as oval containers, for example, are to be inspected, these systems are not readily applicable.
There remains, therefore, a real and substantial need for an automated means of rapidly inspecting dielectric containers which have a generally oval configuration.